288 NATATORES. 



its size and strength it is perhaps the most powerful in the 

 water of all British birds with which we are acquainted. 

 Besides the almost impenetrable covering of feathers, this 

 bird is coated under the skin with a thick layer of fat ; indeed 

 an accumulation of that substance, which is a very imperfect 

 conductor of heat, and therefore well calculated for pre- 

 serving uniformity of temperature, and a consequent healthy 

 state, is common to most warm-blooded animals that live 

 much in the water. 



THE BLACK-THKOATED DIVER (Colyml)US arctlCUS). 



This, like the former, is a rare bird, and rather a straggler 

 than a regular visitant upon the English shores; but it 

 breeds upon the shores of the secluded lakes and pools in 

 some of the more remote islands. 



The length of this species is between two feet and two feet 

 and a half, and the breadth from three feet to three feet 

 eight, but it is more slender, and not so heavy in proportion 

 to its length, as the northern diver. The bill is more than 

 three inches long, rounded and rather blunt at the tip. In 

 the mature bird, the forehead has a stripe down the front of 

 the neck ; the back and rump are black. The sides of the 

 neck, the scapulars, and coverts, thickly spotted with white. 

 The crown and back of the neck grey ; the quills dusky ; 

 the tail black, the feet dusky brown with a pale tinge on the 

 inner sides ; the under part white. The young, like those of 

 the last species, do not receive the mature plumage till the 

 third year. The under part is at first all dusky brown ; the 

 grey on the head, and the black marks on the sides of the 

 neck, appear the second year ; and the black on the throat, 

 and the black and white on the back and scapulars, appear 

 the third year. Birds in all the three plumages, and in the 

 intermediate stages, are seen together, so that the bird has 

 sometimes been described as three distinct species. Its 



